1. Field of the Invention
The present invention relates to accurately positioning blades in a multiple blade assembly for dicing wafers and other substrates used in the manufacture of electronic devices. More specifically, the present invention teaches an apparatus for accurately positioning an edge of each blade in a multiple blade assembly, irrespective of the individual blade thicknesses.
2. State of the Art
In order to manufacture carrier substrates (e.g., circuit boards, interposers, etc.) and semiconductor dice in quantity, a large-scale substrate comprising a large number of unsingulated units is typically processed en masse, then the units separated from one another, typically by sawing the large-scale substrate. In the case of carrier substrates, the large-scale substrate may be either a single-layered or laminated organic substrate, such as FR-4 board, upon which a number of carrier substrates are formed. Semiconductor dice may be fabricated on a wafer or other large-scale semiconductor substrate. The dice may then be scribed or sawn into individual dice. Singulated carrier substrates and semiconductor dice are often used in finishing operations, including packaging. As the state-of-the-art densities of carrier substrates and semiconductor dice on their respective large-scale substrates are ever increasing, the need for accurate rigid placement of dicing saw blades is apparent.
Semiconductor wafers and other substrates are typically manufactured with a multitude of semiconductor devices. Typically, individual semiconductor devices are attached to a carrier substrate via tape-automated-bonding (“TAB”), wire bonding, or flip-chip type solder bonding techniques, the latter often effectuated with so called ball grid array (BGA) configurations of discrete solder balls. Consequently, individual semiconductor devices must be singulated, or separated from each other for use, packaging, and mounting on carrier substrates such as printed circuit boards. Furthermore, the singulated devices may be encapsulated or otherwise “sealed” to protect the electrical connections and chip from environmental damage or contamination.
In order to singulate or perform “dicing” operations on large-scale substrates, dicing saws are typically used. Apparatus for dicing wafers and other substrates usually comprise at least one saw blade attached to a spindle, which rotates via a motor attached thereto. Also, during cutting, cleaning fluid such as de-ionized water is communicated to the substrate and saw blade to wash away cuttings of the substrate material and cool the saw blade.
Increasingly, rapid manufacturing methods include multiple or “gang” saw blade assemblies. In addition, due to semiconductor device and carrier substrate density on the respective large-scale substrate and the attendant necessity for making cuts between the semiconductor devices or carrier substrates as narrow as possible, the individual saw blades are relatively thin. Further, in order to exact precision cuts with reduced forces on the substrate during cutting, dicing saw blades are rotated at relatively high speeds, up to 60,000 revolutions per minute. Dicing saw blades may also be termed “wear blades”, and may include diamond grit proximate their outer edges, although other hard, natural and synthetic particulate materials may be used. Some examples of dicing saw blade materials include: diamond grit encapsulated in resin, diamond grit encapsulated by an electro-deposited nickel film, and diamond grit held in a soft metal. Resin bonded diamond grit blades may be about 0.025 mm to about 0.380 mm thick (e.g., 0.260 mm thick) and about two or three inches or more (e.g., 4.5 inches) in diameter.
Saw blade flexibility is also a concern, because it directly affects deflection and movement of the cutting edge out of the desired vertical plane perpendicular to the substrate, such deflection being known in the art as “run-out”, during cutting. To obtain trueness and stability during cutting, and to minimize run-out, the blades are typically mounted between two flanges so that only a small cutting edge at the outer periphery of the blades is exposed. It has been observed that the maximum depth of cut of the blade held by a flange is limited by the flexibility of the blade.
Due to the extreme processing requirements of dicing saw blades, as well as the increasing density of semiconductor devices on substrates and wafers, as well as the fine tolerances between adjacent carrier substrates or other electrical assemblies (dice) formed on large-scale substrates, accurate placement and control of dicing processes and apparatus is extremely important.
For instance, U.S. Pat. No. 5,571,040 to Kawaguchi et al. discloses a method and device for detecting and controlling the run-out of a flat ring blade member of a slicing machine. Kawaguchi et al. discloses measuring an axial load, calculating a deflection value for the blade, then adjusting for the calculated run-out.
U.S. Pat. No. 5,259,149 to Klievoneit et al. discloses an apparatus and method for grinding opposed faces of the hub of a dicing saw blade flat and parallel while preserving the capability of electroplating the hub with a membrane. Thus, Klievoneit et al. addresses accurate positioning of dicing saw blades, as well as methods of manufacture. However, the Kievoneit et al. process is expensive due to the increased processing time and materials, thus increasing the cost of dicing saw blades.
In addition, U.S. Pat. No. 4,180,048 to Regan discloses a cutting wheel for dicing semiconductor wafers. FIG. 1 and FIG. 2 of Regan show the cutting wheel in detail, including a thin layer of elastomer in contact with the cutting wheel or blade. FIG. 1 and FIG. 2 of Regan have been adapted as FIG. 1A and 1B, respectively. Configuring the blade to be in direct axial contact with an elastomer is undesirable as it reduces the stiffness of the mounted blade. In addition, the elastomer is not constrained on the outer radial periphery, allowing for flexure in the dicing saw blade.
Referring to FIG. 1A, dicing saw blade 50 is installed on flange 5 and held thereon by retaining element 4. Flange 5 is configured to accommodate dicing saw blade 50, compliant layer 2 and retaining element 4 within the axial thickness of the flange 5. Compliant layer 2 is placed between retaining element 4 and dicing saw blade 50, retaining element 4 being held compressively against dicing saw blade 50. Retaining element 4 may be installed on a spindle (not shown) by way of bore 7. The spindle (not shown) may be threaded on one or both ends for applying axial compressive forces to retaining element 4, thus holding dicing saw blade 50 in place. Other compression elements as known in the art may be employed to compress the assembly.
Flange 5 along the radial tip of the dicing saw blade 50 may be tapered, as may the radial tip of retaining element 4, as shown in FIG. 1B. Tapering the retention means of the dicing saw blade 50 gives axial clearance to each side of the dicing saw blade 50 when compared to nontapered alternatives. Compliant layer 2 is located between retaining element 4 and dicing saw blade 50. Thus, during cutting, the dicing saw blade 50 is axially supported on one side by flange 5 and on the other side by retaining element 4 and compliant layer 2. Multiple assemblies of dicing saw blades 50, retaining elements 4, and flanges 5 may be axially positioned adjacent to each other to form a multiblade assembly.
Industrial Tools Incorporated (“ITI”) employs a dicing saw blade spacing apparatus that uses a series of circumferentially unconstrained rings to hold the blade in place. A compression ring of stiff, yet resilient material and retention spacer adjusts for the thickness of the dicing saw blade. The resilient material is not, however, constrained about its outer circumferential surface. This configuration allows for the blade to deflect more easily. In addition, ITI utilizes a series of spacers and fixtures to fix each blade position, which may increase costs and complexity of the apparatus. FIG. 2 illustrates the system developed by ITI.
FIG. 2 shows an assembly including multiple dicing saw blades 50. Moving left to right in FIG. 2, a first retention element 6 provides a seating surface for dicing saw blade 50, where dicing saw blade 50 is radially supported by spacer 16. Contact spacer 18 is positioned axially adjacent to dicing saw blade 50 between dicing saw blade 50 and compliant element 12. A second retention element 6 is positioned and compressed against compliant element 12, in lateral contact with spacer 16. Multiple dicing saw blades may be positioned by repeating the aforementioned elements as shown for a second dicing saw blade 52.
Systems for mounting dicing saw blades, shown in FIGS. 1A, 1B, and 2, may compensate for varying diamond dicing saw blade thicknesses in a multiple dicing saw blade assembly. However, the foregoing systems require that the compliant element or layer have a large, ring-shaped configuration to facilitate radial placement thereof by its inner diameter since neither of the illustrated configurations radially peripherally constrains the compliant element or layer. Such configurations limit the design alternatives of the compliant element.
Although diamond saw blades may be very accurately manufactured via lapping technology, increased blade thickness accuracy also increases the cost of the dicing saw blades. Furthermore, little advantage in the way of durability or improved life is gained by such accurate tolerances. Accordingly, it would be advantageous to use dicing saw blades with varying thickness while retaining accurate and rigid axial positioning of each dicing saw blade in a multiple dicing saw blade assembly.
Thus, it can be understood that accurate and rigid positioning of dicing saw blades of variable thicknesses is of great importance in the manufacture of semiconductor devices. In addition, it is desirable to eliminate the locational effect of the variation in the thickness of the dicing saw blades on the axial locations of other dicing saw blades in a multiple dicing saw blade assembly.